Methylglyoxal-induced increase in peroxynitrite and inflammation related to diabetes
Methylglyoxal (MG) is a reactive α-oxoaldehyde and a glucose metabolite. Previous studies in our laboratory have shown that MG induces the production of reactive oxygen species (ROS), such as superoxide (O₂˙¯), nitric oxide (NO) and peroxynitrite (ONOO¯), in vascular smooth muscle cells (VSMCs, A-10 cells). However, the effect of endogenous MG and mechanisms of MG-induced oxidative stress have not been thoroughly explored. The present study investigated fructose (a precursor of MG)- induced ONOO¯ formation in A-10 cells and whether this process was mediated via endogenous MG formation; roles of MG in regulating mitochondrial ROS (mtROS) production and mitochondrial functions in A-10 cells; and effect of MG on neutrophils in patients with type 2 diabetes mellitus (T2DM). Fructose induced intracellular production of MG in a concentration- and time- dependent manner. A significant increase in the production of NO, O₂˙¯, and ONOO¯ was observed in the cells exposed to fructose or MG. Fructose- or MG-induced ONOO¯ generation was significantly inhibited by MG scavengers and by O₂˙¯ or NO inhibitors. The data showed that fructose treatment increased the formation of ONOO¯ via increased NO and O₂˙¯ production in A-10 cells, and this effect was directly mediated by an elevated intracellular concentration of MG. By inhibiting complex III and manganese superoxide dismutase activities, MG induced mitochondrial overproduction of O₂˙¯, and mitochondrial ONOO¯ further. MG also reduced mitochondrial ATP synthesis, indicating the dysfunction of mitochondria. In addition, MG increased plasma NO levels in patients with T2DM, which reflected the oxidative status in those patients. MG-induced oxidative stress in patients with T2DM significantly enhanced levels of cytokines released from neutrophils. Moreover, the neutrophils from T2DM patients showed a greater proclivity for apoptosis, which was further increased by in vitro MG treatment. Our data demonstrate that MG-induced oxidative damage, particularly ONOO¯ production, contributes to the pathogenesis of T2DM and its vascular complications.
Peroxynitrite, Methylglyoxal, Mitochondria, Type 2 diabetes, Smooth muscle cell
Doctor of Philosophy (Ph.D.)